Printed electronics which have been recently researched a lot means manufacturing electronic devices and components or modules through a printing technique. That is, electronic products having desired functions are manufactured by printing conductive or functional ink on a substrate such as plastic, papers, glass, and silicon.
The printed electronic process is easy to apply a method (roll-to-roll, R2R) of performing printing while winding a flexible material such as a film around a rotating roll. Since the printed electronic process is suitable for a large area and high-speed mass production, production costs may be reduced up to 1/10 as compared with an existing process, and the printed electronic process has an eco-friendly characteristic because a use amount of materials wasted in an existing silicon-based process or toxic materials, energy consumption, and the like may be largely reduced.
A representative printed electronic technique includes an inkjet printing method, a gravure printing method, a screen printing method, and the like.
Among them, the inkjet printing method is a process technique of ejecting minute ink drops (having a diameter of 30 μm or less) from a head to pattern the ejected ink drops at a desired position. This technique is known as a process technique suitable for implementing a complicated shape in a small volume by a contactless method, and a basic technique has been developed as a printing technique of papers, and has been remarkably developed lately enough to perform high resolution printing. Application fields of the technique have been largely expanded from computers in offices and home to commercial printing, industrial printing, display or electronic circuit fields, and bio fields such as DNA chips.
The inkjet printing method has advantages in that a process is simple, and equipment costs and manufacturing costs may be reduced. Since the material is deposited at a desired pattern position, in principle, there is no loss of the material, and as a result, there is no waste of raw materials and an environmental load is small. Since a process such as developing and etching is not required like photolithography, properties of substrates or materials are not deteriorated by a chemical effect, and a device is not damaged due to a contact because of a contactless printing method, and patterns may be formed on a substrate having unevenness. In the case of printing by a drop on demand (DOD) method, a pattern shape may be directly edited and modified by a computer. On the contrary, the inkjet printing method has a disadvantage in that a printing speed is low because the patterns are formed in sequence. As a result, for a high-speed printing of LCD color filters, LCD companies such as Sharp Corporation, Samsung Electronics Co., Ltd. and LG Philips-LCD have developed multi-nozzles, high density of nozzles, high frequency of driving frequency, and the like.
The gravure printing method, as a kind of printing method using an intaglio, is a method of transferring ink put in a concave portion to a printed matter, after coating the ink on a cylindrical plate having unevenness to scrape the ink coated on a convex portion. In a conventional method, after photosensitivity is applied to a surface of a cylinder, a plate is made by overlapping and engraving a gravure screen and a transparent positive and performing etching with a ferric chloride solution. Since the surface of the plate is constituted by minute half-tone dots divided by a screen line to be deeply etched in proportion to the concentration of an etching solution, grays of a minute pattern may be reproduced to be widely used for printing of magazines or catalog pictures. Since the printing concentration is determined by a depth and density of minute pores, a coating thickness is easily controlled and the method is effective when the device is manufactured. A gravure offset printing method of coupling the printing method and an offset printing method has been recently applied for wirings of displays of LCD color filters and electronic circuits. The gravure offset printing method is an offset printing method of performing printing by transferring ink from a printed plate to a rubber blanket and transferring the ink of the blanket to the substrate again and a printing method of replacing a printed plate of the offset printing method with a printed plate used in the gravure printing method. Japanese companies such as Dai-Nippon Print or Toppan Print had discussed the gravure printing as an important manufacturing process of a flexible organic electronic device together with a screen printing method, and particularly, had expected that the gravure printing is useful to manufacture a minute printed electronic device of several μm or less.
The screen printing method is illustrated in FIG. 3 as a process of loading an ink paste on a screen pulled by strong tension and pressing and moving a squeegee to push and transfer the paste to the surface of the printed matter through a mesh of the screen. Similarly to the inkjet printing method, as an additive process having a small loss of the material, researches for manufacturing displays such as an active matrix organic light emitting diode (AMOLED) are being conducted. The screen originally uses fabrics such as silk, but a mesh material for minute patterning is changed to stainless steel, and the used paste is used by dispersing a resin or solvent in a basic material such as metal powder or semiconductor because proper viscosity is required. Although the screen printing method is a contact printing method in which the screen contacts the substrate to transfer the paste while a distance of several mm is maintained between the screen and the substrate and then the squeegee passes between the screen and the substrate, there is no effect of the substrate through contact.
A market of printed electronics is still in its early stages, but is expected to be rapidly expanded in accordance with the development of material and process techniques and advanced demands, and the printed electronics have potential capable of causing a revolution in almost all fields in which semiconductors such as RFID tags, illuminations, displays, solar batteries, batteries, or devices, circuits, and the like are used. A high-performance integrated circuit has also possibility to replace an existing silicon-based product. Famous enterprises in related industries field such as electronics, chemistry, and printing are promoting development and commercialization, and widespread applications are possible up to security services, packaging and distribution, environment/energy, healthcare industries in addition to an electronic industry.
However, the printed electronic technique in the related art has shortcomings and limitations, and among them, a lack of performance and integration is the most remarkable. Due to the limitations of material and process techniques, a thickness of a thin film is large, a surface state is bad, and performance and integration are inferior as compared with existing electronic devices or manufacturing methods. There is a problem in that durability is relatively low because organic printing materials have low durability as compared with existing inorganic materials, and therefore research and development (R&D) for inking of high-performance inorganic materials and performance improvement of organic materials is required.